1. Field of the Invention
The present invention relates to a frame structure for a buggy such as a four-wheeled buggy for use on rough terrain, a method of manufacturing such a frame structure, and a jig for use in manufacturing such a frame structure.
2. Description of the Related Art
Suspension structures for use with a frame structure which supports front wheels of a four-wheeled buggy with a rider's saddle are known from Japanese patent publications Nos. 6-92237 and 7-88127, for example. The disclosed frame structure includes a pair of laterally spaced lower frames extending longitudinally of the frame structure and a pair of arm brackets mounted on the lower frames. Swing arms are attached to the arm brackets, and a steering bracket is joined to the lower frames. The steering bracket has a holder hole through which a support member is installed. The lower end of a steering shaft is rotatably supported by the support member.
Loads are concentrated on the arm brackets which support the swing arm. However, since the arms brackets are of a relatively small size and only locally project from the lower frames, the arm brackets are reinforced by various stiffening members for maintaining a desired level of supporting rigidity.
Generally, the arm brackets are welded to the lower frames, and the steering bracket is also welded to the lower frames. When one of these brackets is welded, the other brackets that have already been welded are subject to the influence of thermal strain which tends to lower the dimensional accuracy of the other brackets. Therefore, it is necessary to remove such strain that has been introduced by the welding process.
There has been a demand for a frame structure which is capable of distributing loads which would otherwise be concentrated on an arm bracket and for a method of manufacturing such a frame structure through a simplified welding process which does not incur thermal strain with respect to welded regions and can join members with high positional accuracy.